Selec-Trac full time 4x4 4WD system discussions

[Billy]

Looking at these pics, you can see that the Selec-Trac T-case has a set of planetary gears next to the chain drive, which allows an "open" diff in Full Time 4Hi. It also has a set of planetary gears for the reduction in 4Lo. The Rock-Trac has only 1 set of planetary gears, which are not only bigger for more reduction ratio, but definitely heavier duty for strength and durability. Also of note is that the chain drive is quite a but burlier on the Rock-Trac.

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[digitalbliss]

So Selec-Trac allows you to use 4x4 on dry pavement? Does it not cause axle binding / bind up?

Basically, its an AWD system.

 

[WaltA]

Yes and no...

The Select-Trac in my Liberty had 2Hi, PT4Hi, FT4Hi, and 4L.

My current WK has full time 4WD, with a little cheesy swith to go into Neuter (sic) or 4L.

It was the same as with your Liberty, in my XJ that had SelecTrac (and Back Country).

As I posted earlier, I don't understand why having a FT4Hi, and a PT4Lo with a 4:1 ratio, have to be mutually exclusive.

 

[The Great Grape Ape]

I just want to know if in 4low is it fully locked up, no slipping, gear to gear contact like the current 4x4 system is?

Yes, it's still chain driven with a 6 element planetary gear setup that allows true locking when in 4Lo and 4Hi PT.

 

[The Great Grape Ape]

Ya, see how your Liberty has Selec Trac (part time 4wd), but your WK Grand Cherokee has full time 4wd (Quadra Trac). Nominally, they are different. I'm no Jeep engineer, but I wonder what differences are between the two.

No the Liberty had the NP(NV)242, which is the ream of the crop of selec-trac. The Hummer H1 & H2 used a beffier version of the NV242 throughout its life, and there are Wrangler swap kits and upgrade kits from folks like Tom Woods.

The 70s QuadraTracs were the lesser NP219 and NP228, the NP/NV242 is the perfect fit for a Wrangler with FullTime 4WD and true locking PT 4WD.

Something really good like the Land Cruisers...

Hopefully better than that... hopefully something more like the NP/NV242.

 

[The Great Grape Ape]

Hmmmm... don't know how I feel about the chain drive. That's not how it is now is it? I didn't think it was? What are your thoughts on it? Speaking about real off roading here.

Yes the NV241(OR) is also chain driven, but the SelectTrack NP242 adds a 6-element planetary gearset and a 48/52 torque biased diff to add the FulltTime component.

If the SelecTrac is like the NV242, then it's truly the best of both worlds., with true LOCKED 4WD as well as forgiving FT 4WD for wet/snowey/icey pavement to from the trail / ski hill.

 

[The Great Grape Ape]

As I posted earlier, I don't understand why having a FT4Hi, and a PT4Lo with a 4:1 ratio, have to be mutually exclusive.

I answered back in the other thread, it doesn't need t be mutually exclusive, it just so hapoens it's always been 2.72:1 even on the Hummer, and for practical 'trim-level' consistency aspect, it's easier to pick engine/axle/tire combos from FCA's perspective if the Sahara (and Special Edition) options are confined to similar 2.72:1 CommandTrac or SelecTrac.

There's no reason they couldn't change the gearset and make a 4:1 variant, but from a practical standpoint, their first focus would likely be for the 2.72:1 variant that puts it in their biggest selling mid-range platforms, and then afterwards if it's well received and does well in the wild, then offer an upgraded version.

Personally I'd love/prefer a 4:1 version as it would allow me to be milder on the axle for day to day use, and to reduce traction-loss at icey intersections, etc. (I'm not trying to impress anyone or blow their doors off at the lights) but then it also allows me to turn things up a notch when truly needing to go 4Lo. I just don't think it's FCA best first option solely from a production consistency consideration.

 

[Dart Maul]

Interesting news. I guess FCA knows their Sahara buyers. This will be a big seller and very useful for bad weather and rough roads but it is not meant for true off roading.

 

[The Great Grape Ape]

Interesting news. I guess FCA knows their Sahara buyers. This will be a big seller and very useful for bad weather and rough roads but it is not meant for true off roading.

Why would you say that? It's not a weak transfer case, and it has all the options the of the current command-trac, plus FT 4WD, how is that a minus?

Even the 4Lo ratio is less of an issue vs current NV241OR (same as regular 241) thanks to the new higher 1st gear ratio and larger overall spread in the new ZF-8 transmission.

A new JL Shara with Selec-Trac would be a better off-roader than a current Sport or Sahara JK even if those were the only 2 improvements.

 

[WXman]

Well, first of all, they are using the Selec-Trac name. Which implies that it'll be the NV242 design. I had it in my KJs (behind the diesel engine) and my ZJ (behind the 4.0) and had zero failures. Both of those engines were known as torquey engines, and I had no problems and didn't know anyone else who did either. The Selec-Trac is the best t-case ever offered because it has all the settings that Command-Trac had, but it added the full time setting that could be used on pavement for rainy or snowy weather. By calling this a "full time" system...they're simply pointing out that it has a full time setting, something Wrangler has NEVER had in the past.

Secondly, we must remember that historically, first model year vehicles are usually one-off. This is particularly true of Jeep. We always always see drastic changes starting in model year #2 in terms of equipment availablity, packages, trim level content, etc. So my guess is that Selec-Trac will be expanded to other trims for 2019. And...if you want a stick shift you better buy one because if the manual transmission doesn't sell well, it'll be axed soon.

 

[Thau]

First Post:

4WD Part time is 4WD high. The T-Case is splitting power all the time without the clutch. Binding of the wheels will occur on dry roads or high traction surfaces
4WD Full time is also 4WD high but with a spring loaded clutch to allow for slip on dry pavement

I had 114K miles in my 2002 KJ with the Select Trac with zero problems and I drove around in "Full Time" year round for 13 years. I was planning on the Rubi to replace my KJ but now I am torn between the NV242 and a Rubi.

 

[WXman]

Rock-Trac is great...........if you're in the rocks.

On every other terrain it sucks. Most guys hate it. Snow, mud, sand, water crossings, etc....you don't want to be crawling like a snail with a broken leg.

 

[attworth]

Curious what users of a modern Selec-Trac experience as far as fuel economy compared to a standard selectable system.

Coming from a FWD car, I think this might make my wife more confident and safe in the winter time.

 

[digitalbliss]

Curious what users of a modern Selec-Trac experience as far as fuel economy compared to a standard selectable system.

Coming from a FWD car, I think this might make my wife more confident and safe in the winter time.

I absolutely think this is the reasoning in putting the selec-trac into the wrangler. Makes even more sense in the JLU Sahara as that is probably the biggest "soccer mom" segment.

 

[The Great Grape Ape]

Well, first of all, they are using the Selec-Trac name. Which implies that it'll be the NV242 design.

I know there was a switch activated Selec-Trac II instead of the lever of the NV242, but I can't find detailed data about it other than a Jeep video on youtube, which isn't very detailed, and gives no hints as to it's underlying model number. However I think ST II wasn't an NP/NV242 (which may be supported by the video's similar looking but different torque split numbers of 42/58 for ST-II vs the ST's 48/52 split), so I'm not 100% confident that the JL gets the NV242, just based on the term SelecTrac, just hoping it does, or at least something exactly like it.



A good list of all the Jeep transfer cases;

http://www.fourwheeler.com/how-to/transmission-drivetrain/154-1201-jp-guide-to-jeep-transfer-cases/

(edited the typo 'level' on the NV242 to the proper "lever")

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